The invention relates to an electric lamp provided with
a translucent lamp vessel sealed in a vacuum-tight manner;
a light source arranged inside the lamp vessel;
current supply conductors extending from the light source through the wall of the lamp vessel to the exterior;
a getter inside the lamp vessel, which comprises an intermediate compound of a first metal with a second metal.
Such a lamp is known from German Offenlegungsschrift 1,905,646.
In the known lamp, the getter is an alloy of at least 5% by weight of at least one metal selected from the group III, IV, V of the periodic table and tungsten with at least one metal selected from the group VIII of the periodic table, and copper, which alloy has a melting point of at most 1250.degree. C. This getter may be inter alia an zirconium/nickel alloy containing 5% by weight of Zr or Zr.sub.2 Ni, which latter alloy contains 75.7% by weight of Zr. The getter serves to bind oxygen in the lamp.
In various types of lamps, however, water is a very harmful impurity. This substance may be present in a large quantity in lamps having a lamp vessel which is coated electrostatically with a powder. In order for a lamp vessel to be coated electrostatically, the resistivity of the powder this resistivity to be applied is of importance and the value is strongly influenced by the moisture content of the powder. Thus, by coating a lamp vessel electrostatically moisture is introduced into the lamp vessel.
In a lamp having incandescent tungsten parts, for example a filament, water can produce tungsten oxide and hydrogen. The oxide can evaporate and be deposited on the wall of the lamp vessel. Tungsten oxide may also react with the hydrogen to form tungsten, which is deposited at colder areas, and water. Consequently, water is the carrier of a cycle process, in which tungsten is transported from the filament to colder areas. This leads to a reduced transmission of light and to an accelerated disintegration of said filament and a short life of the lamp.
Hydrogen, for example hydrogen obtained by decomposition of water, may lead to reduction of glass metal connections, as a result of which a lamp vessel becomes leaky along current supply conductors and the lamp fails prematurely. Hydrogen may further cause flashover, for example in evacuated lamp vessels, or may penetrate through a quartz glass wall into a discharge vessel and lead to an increase of the ignition voltage of the discharge arc.
Oxygen in a lamp may lead to an undesired oxidation.
Water on a harmful substance in lamps because its harmful effect is stronger than that of oxygen and hydrogen together. It is therefore of great importance that means are available by which water can be bound. Furthermore, it is of importance that, when binding water, no hydrogen or oxygen is formed which is not also bound. It is also of importance that means are avaiable which are capable of binding molecular oxygen and hydrogen.